1. Field of the Invention
The present invention relates generally to a prerinse for a yttrium-containing electrodepositable coating composition.
2. Background Information
Electrodeposition as a coating application method involves depositing an electrodepositable coating composition onto a conductive substrate, which is under the influence of an applied electrical potential. Electrodeposition has become increasingly important in the coatings industry because, by comparison with non-electrophoretic coating means, electrodeposition offers increased paint utilization, improved corrosion protection, and low environmental contamination.
During electrodeposition, the electrodepositable coating composition is deposited onto a substrate that has been pretreated with a pretreatment solution, such as a zinc phosphate pretreatment solution, prior to the electrodeposition process. The pretreatment step may provide an additional degree of corrosion protection to the substrate material as compared with untreated substrates. Elimination of the pretreatment step prior to the electrodeposition process would reduce the costs associated with coating a substrate as well as eliminate any chemical byproducts that are produced during the pretreatment step. Moreover, in an automotive OEM factory setting, elimination of the pretreatment equipment would mean that the size of the factory could potentially be scaled down or that valuable factory space could be reclaimed.
One approach to this problem is to modify the composition of the electrodepositable coating to include materials that provide corrosion resistance to the substrate material without the need for a pretreatment step. For example, the element yttrium, added to conventional electrodeposition coatings, has been found to provide improvement in corrosion protection to cold rolled steel (“CRS”) without the need for a pretreatment step. To further improve adhesion and to limit the amount of yttrium in the electrodeposition coating, as provided in U.S. patent application Ser. No. 12/693,626, which is herein incorporated by reference, a yttrium-containing electrodepositable coating composition that does not require a pretreatment included a film-forming polymer, yttrium, and a silane material in various forms.
The present invention is directed to a method for further enhancing corrosion protection to non-pretreated substrates coated with a yttrium-containing electrodepositable coating composition.